Added a strftime :format option for the month name

Added a helper ```add_format_option(options)``` that will help when deprecating those annoying options for ```month_name```. Now, you can pass in a ```:format``` option that is a string that Date.strftime will accept.
http://www.ruby-doc.org/stdlib-2.1.1/libdoc/date/rdoc/Date.html#method-i-strftime

I also deleted some private helpers that were not being used anymore after the refactor.

/cc @senny @matthewd